冻融条件下玄武岩纤维混凝土断裂韧度研究

该文使用数字图像相关方法实时观测三点弯试验中切口混凝土梁全场变形，分析混凝土梁断裂破坏过程中水平位移和应变的变化规律，基于切口处水平位移和应变变化规律确定起裂荷载，并研究冻融循环次数和纤维掺量对混凝土起裂韧度、失稳韧度、临界开口位移的影响，结果表明：对于C30混凝土而言，起裂韧度和失稳韧度随冻融次数的增加而减小，降幅约为0.6 MPa·m^1/2~0.80 MPa·m^1/2，两种韧度随玄武岩纤维掺量增加有小幅增加，最大增幅分别约为0.1 MPa·m^1/2和0.2 MPa·m^1/2，说明玄武岩纤维能提高C30混凝土的抗冻性，但提高程度是一定的，玄武岩纤维不能完全抑制冻融对混凝土的损伤；纤维掺量对失稳韧度的提高幅度要比起裂韧度大；起裂韧度增益比和失稳韧度增益比都随纤维掺量增加先增大后减小，两种韧度增益比均在纤维掺量为2.0 kg/m³时最大，因此，在混凝土强度等级为C30时，2.0 kg/m³可作为最佳纤维掺量；临界开口位移随冻融次数增加而增大，随纤维掺量变化效果不明显，与纤维增强作用相比冻融损伤是影响断裂过程变形性能的主要因素；最后在试验结果的基础上，建立了起裂韧度和失稳韧度随纤维掺量和冻融次数的拟合模型。

FRACTURE TOUGHNESS OF BASALT-FIBER REINFORCED CONCRETE SUBJECTED TO CYCLIC FREEZING AND THAWING

The law of horizontal displacement and strain strange in the fractured process of concrete beams was analyzed through the real-time observation of deformation to the incision concrete in a three-point bending test by using a digital-image-correlation method. Based on the law, the crack loads could be determined. The effects of freeze-thaw cycles and the fiber content on the fracture toughness, the instability of toughness, and the critical opening displacement, were studied. The results show that for grade C30 concrete, the fracture toughness and instability toughness, which reduced by 0.6 MPa·m1/2~0.80 MPa·m1/2, decrease with the freeze-thaw cycles, and that to the contrast, slightly increase about 0.1 MPa·m1/2 and 0.2 MPa·m1/2 with the mixed basalt-fiber volume. And basalt fiber can improve the frost resistance of grade C30 concrete, but the degree of increase is limited. Basalt fiber cannot completely inhibit the damage of concrete subjected to freezing and thawing. The raise of instability toughness with basalt-fiber volume is larger than that of fracture toughness. The crack and instability toughness gain ratio, which were the largest with 2.0 kg/m3 fiber content, was increased first and then decreased. Therefore, 2.0 kg/m3 can be used as the optimal fiber content of strength grade of C30 concrete. Critical opening displacement increases with the freeze-thaw cycles, but not obviously with the fiber. Compared with the effects of the fiber, the significant factor of the deformation in the process of fracture is the damage of freeze-thaw cycles. Finally, according to the experiment, the fitting model is established for the crack and instability toughness with the fiber content and freeze-thaw cycles.